The main effort continues to be site-specific studies of tumor risk in a cohort of 120,000 Hiroshima and Nagasaki A-bomb survivors. Radiation-related tumors of the CNS, salivary gland and skin are largely confined to a relatively few cell types. Analyses of female breast cancer incidence show a high excess relative risk for women exposed before age 20, that continues undiminished over time following exposure. The only exception is an anomalously high excess for risk of early-onset cancer, diagnosed before age 35. At an NCI-sponsored, international workshop held in Hiroshima, it was agreed that this anomaly presents the most promising possibility of a radiation-host factor interaction involving a genetically predisposed subgroup. Actions being taken include (1) development of a family database for the study cohort, (2) cataloging of available tissue samples from relevant subjects, (3) immortalization of cell lines from stored and fresh blood specimens, and (4) closer involvement in the A-bomb survivor studies of scientists from the DCEG Genetics Program.